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RF Sounding: Generating Soundsfrom Radio Frequencies

Claudia Rinaldi, Fabio Graziosi, Luigi Pomante and Francesco TarquiniCenter of Excellence DEWS, University of L’Aquila

Italy

1. Introduction

In this chapter we present an innovative way of exploiting technological innovations broughtby Wireless Sensor Networks (WSNs) functionalities and cellular communications in twoimportant social fields: art and education. The result is an artistic installation built throughthe use of innovative technologies that can also be used with educational purposes.

In recent years there has been a growing interest on the theme of multidisciplinarity aswell as exploitation of new technologies in the artistic field. Artistic installations andperformance have exploited the most recent technological innovations, introducing newneeds and requirements to be satisfied from a scientific point of view.

On the other hand the problem of the electromagnetic pollution has recently become animportant theme of discussion for both scientific and media communities and it has oftenbeen faced with incomplete, where not wrong, knowledge of the phenomena involved. Thisis especially true while concerning with cellular networks where the most popular belief isthat transmitting antenna produce the most of the electromagnetic radiation. RF Soundingwill provide the user with the possibility of understanding the real behaviour of cellularcommunications in terms of RFs transmission power.

A classification of interactive art installations, organized according to which softwaretechnology (like for example MAX/MSP) and software engineering processes have beenused, is presented in (1). (2) presents the software engineering process that has lead to thedevelopment of Flyndre, an installation at the coast of Norway, where the composition ischanged according to weather parameters. In this respect, (3) presents the technological andartistic processes around Sonic Onyx, an installation in Trondheim where the audience cansend Bluetooth files, which are reconstructed to new sound compositions and played.

The usefulness of technology into art expressions and education has also been demonstratedin two projects from MIT. Musicpainter, (4), is a networked, graphical composing environmentthat aims to encourage sharing of music creation and collaboration within the composingprocess. Indeed a composer could start with a small idea (e.g. only rhythmic or melodic),share it in the network and receive suggestions from other composers. TablaNet, (5), is anintelligent system that listens to the audio input at one end and synthesizes a predicted audiooutput at the other, when live music event where musicians are located remotely from each

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other. Other examples of artistic performances that are possible because of technology are theones presented by the Opera of the Future Group from MIT media lab, (6). For instance "Death

and the Powers" is a groundbreaking opera that brings a variety of technological, conceptual,and aesthetic innovations to the theatrical world. Musical performances with educationalpurposes too are also possible by using Reactable, (7), an electronic music instrument realizedby the Music Technology Group of Pompeu Fabra University of Barcelona. While concerningwith the possibility of enabling a joint reserach in both artistic and technological fields,the Allosphere project has also to be cited, (8). Allosphere is the result of 26 years ofresearch and it allows visualizing, hearing and exploring complex multi-dimensional data.Scientifically, the AlloSphere can help provide insight on environments into which the bodycannot venture. Artistically, the AlloSphere can serve as an instrument for new creations andperformances fusing art, architecture, science, music, media, games, and cinema. Anotherrelated multidisciplinary application is the field at the intersection between adaptive musicand games. For example, (11) presents an experimental application for individualizedadaptive music for games.

Between the different technological innovations suitable for artistic purposes, Wireless Sensor

Networks (WSNs) are used very often. For instance Spheres and Splinters is a new workcomposed by Tod Machover for hypercello, electronics, and responsive visuals that exploitsaudio analysis and a multitude of wireless sensors on the cello and the bow that capture howthe instrument is being played. WSNs are used for personal purposes in (9) where the basicidea is to generate soundtracks for portable music players basing on the activity the user iscarrying on. This way a proper music for exercise can be available to the user without theneed for him to choose.

The main advantages deriving from the use of WSNs in such an application field is given bytheir flexibility and suitability for temporary network setups. Moreover implementation costis cheaper than wired network even if they are more complex to configure and sometimes maybe affected by surrounding events.

Advantages of using WSNs can be exploited for various purposes such as militarytarget tracking and surveillance, natural disaster relief, biomedical health monitoring, andhazardous environment exploration and seismic sensing, (10). In military target trackingand surveillance, a WSN can assist in intrusion detection and identification. With naturaldisasters, sensor nodes can sense and detect the environment to forecast disasters before theyoccur. In biomedical applications, surgical implants of sensors can help monitor a patient’shealth. For seismic sensing, ad hoc deployment of sensors along the volcanic area can detectthe development of earthquakes and eruptions. With the main goal to provide secure livingenvironments for people in the world, a class of approaches refers to the exploitation ofwireless sensor networks for surveillance purposes, (16).

2. RF sounding overview

This section is intended to introduce the main components of the project as summarized infigure 1. Innovations introduced and novelty will be described in detail in the next sections.

RF Sounding is an artistic installation whose aim is twofold. Indeed from one side we wantto increase end users knowledge of the strength of the power emitted by their cellular phones

46 Management of Technological Innovation in Developing and Developed Countries

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RF Sounding: Generating Sounds from Radio Frequencies 3

Fig. 1. RF Sounding-dataflow diagram.

with respect to the electromagnetic fields produced in the environment, on the other handwe want to provide for an artistic and interactive installation that can also be remotely joinedthrough a web interface. It is worth noting that everything is based on the conversion of RadioFrequencies (RFs) that can be registered inside the area, into audible sounds that are spreadall over the installation space through a sound diffusion system.

Here follows a brief description of the installation’s architecture. Axonometric views of theproject are provided in figures 2 and 3, while a block diagram is given in figure 1.

RF Sounding is built inside a hexagonal area that is accessible through at least 2 entrancesequipped with gating sensors; these are intended to provide user entrance information. Aloudspeaker is placed on each vertex of the hexagon in order to exploit sound spatialization.Along with the speakers there are three or more wireless sensor nodes that feed a positioningalgorithm allowing to evaluate the user position and movement in the equipped area. Thesesensors thus allow the installation to interact with user’s movements by changing lights andsounds conditions. In the center of the hexagon, at a level of 2.5-3 m from the ground, areceiving antenna is placed in order to gather all signals in the band of interest and to sendthem to a spectrum analyser. The analyser is linked to an elaboration unit, equipped with anaudio processing board, that implements sound’s elaboration and spatialization algorithms.This unit also handles the processing of the localization data obtained from the WSN. RFSounding thus allows a user that enters the installation area bringing his switched off mobilephone, to perceive a low intensity acoustic signal that can be associated to RF signals emittedby far sources such as Base Stations (BSs) or other Mobile Terminals (MTs). On the other handif the user inside the equipped area switches on his cellphone, he will sense a much higheracoustic signal.

3. From RF to audible frequencies

In this section we describe the process used to transform radio frequencies coming fromcellular networks, into audible frequencies. The first subsection is intended to briefly reviewfrequencies utilization and organizations in GSM and UMTS standards, the second subsectionproposes an example of two cellular networks procedures that are transformed into soundevents, while the third subsection goes deeper inside the translation procedure for bothstandards.

47RF Sounding: Generating Sounds from Radio Frequencies

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Fig. 2. RF Sounding-axonometric view.

Fig. 3. RF Sounding-axonometric view with details.


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System Band Uplink (MHz) Downlink (MHz) Channel numberT-GSM-380 380 380.2-389.8 390.2-399.8 dynamicT-GSM-410 410 410.2-419.8 420.2-429.8 dynamicGSM-450 450 450.6-457.6 460.6-467.6 259-293GSM-480 480 479.0-486.0 489.0-496.0 306-340GSM-710 710 698.2-716.2 728.2-746.2 dynamicGSM-750 750 747.2-762.2 777.2-792.2 438-511

T-GSM-810 810 806.2-821.2 851.2-866.2 dynamicGSM-850 850 824.2-849.2 869.2-894.2 128-251

P-GSM-900 900 890.0-915.0 935.0-960.0 1-124E-GSM-900 900 880.0-915.0 925.0-960.0 975-1023, 0-124R-GSM-900 900 876.0-915.0 921.0-960.0 955-1023, 0-124T-GSM-900 900 870.4-876.0 915.4-921.0 dynamicDCS-1800 1800 1710.2-1784.8 1805.2-1879.8 512-885PCS-1900 1900 1850.2-1909.8 1930.2-1989.8 512-810

Table 1. GSM bands assignement.

It is worth noting that aesthetic considerations about these procedures are taken into accountin section 6.

3.1 GSM and UMTS frequencies exploitation

The shared global use of the radio spectrum is established by ITU (InternationalTelecommunication Union) (17), that promotes international cooperation in assigning satelliteorbits, works to improve telecommunication infrastructure in the developing world andestablishes worldwide standards.

We first focus on GSM, whose radio technology is specified in the 3GPPTM TS 45.-seriesspecifications, (18), (19). We particularly refer to (19), where frequency bands of GSM systemsare presented.

A GSM system may operate in 14 frequency bands as presented in table 1.

The carrier spacing, that is the channel bandwidth is of 200 KHz.

GSM-900 and GSM-1800 are the most used in Europe and we thus focus on these 2 bands ofinterest. It has to be noticed that GSM uses a variety of channels that are distinguished intophysical and logical channels.

The method to divide up the bandwidth among as many users as possible, chosen by GSM,is a combination of Time- and Frequency-Division Multiple Access (TDMA/FDMA). FDMAdivides the frequency band, which ha a width of (maximum) 25 MHz, into 124 carrierfrequencies. Each Base Station (BS) is assigned one or more carrier frequencies. Using a TDMAscheme each carrier frequency is divided in time, which forms logical channels. More inparticular a channel number assigned to a pair of frequencies, one uplink and one downlink,is known as an Absolute Radio Frequency Channel Number (ARFCN). GSM divides up eachARFCN into 8 time slots. These 8 timeslots are further broken up into logical channels.


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Logical channels can be thought of as just different types of data that is transmitted only oncertain frames in a certain timeslot. Different time slots will carry different logical channels.We underline that RF Sounding does not concern with logical channels since it relies on theuse of a spectrum analyser.

A first prototype of our project that has been developed on 2010, (20), used a GSMengine (Siemens TC35, (21)) that allows to check only for the downlink channel, returninginformation concerning the serving Base Station (BS) channel and the power received (Rxpower) as well as the same parameters for adjacent BSs. With the introduction of the spectrumanalyser we take into account both uplink and downlink physical channels.

GSM standard has been the first to be investigated in the project, subsequently we deepenedproblems and issues arising while considering 3G networks.

UMTS is an evolution of GSM as well as a complete system architecture, offering substantiallyhigher data rates with the main goal of delivering multimedia services in the mobile domain.The process of reserving and allocating frequency spectrum for 3G networks began on 1992during the World Administrative Radio Conference and ended on 1997 with Resolution 212adopted at the World Radiocommunication Conference (Geneva, Switzerland), that endorsedthe bands specifically for the International Mobile Telecommunications-2000 (IMT-2000)specification. According to WARC-92 "the bands 1885-2025 MHz and 2110-2200 MHz areintended for use on a worldwide basis, by administrations wishing to implement InternationalMobile Telecommunications-2000 (IMT-200)". Basing on (22) and (23), UMTS frequencies canbe summarized as follows:

• 1920-1980 and 2110-2170 MHz Frequency Division Duplex (FDD, W-CDMA) Paired uplinkand downlink, channel spacing is 5 MHz and raster is 200 kHz. An Operator needs 3 - 4channels (2x15 MHz or 2x20 MHz) to be able to build a high-speed, high-capacity network.

• 1900-1920 and 2010-2025 MHz Time Division Duplex (TDD, TD/CDMA) Unpaired,channel spacing is 5 MHz and raster is 200 kHz. Tx and Rx are not separated in frequency.

• 1980-2010 and 2170-2200 MHz Satellite uplink and downlink.

CDMA (Code Division Multiple Access) is a spread spectrum multiple access technique whereData for transmission is combined via bitwise XOR (exclusive OR) with pseudorandom codewhose rate is much higher then the data to be transmitted. Moreover UMTS supports bothfrequency division and time division duplexing mode.

Carrier frequencies are designated by a UTRA Absolute Radio Frequency Channel Number(UARFCN). The general formula relating frequency to UARFN is: UARFCN = 5 * (frequencyin MHz).

3.2 Cellular network procedures examples

In this subsection we present two of the procedures that characterize GSM cellularcommunications and that are transformed into an audible sound by RF Sounding.

The first procedure is related to the switch on of a MT inside the equipped area. In absence ofprevious information, the MT starts scanning the radio channels in the service band in orderto find the carrier frequencies emitted by each cell with constant power. Once this procedure


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is completed the MT has a list of all possible BS to which it can connect, and it chooses theBS characterized by the highest receive power (top of the list). Once the carrier frequency isknown, the local oscillator (LO) of the mobile terminal is tuned to this frequency through aphase locked loop operating on a periodically emitted Frequency Burst (FB) (40) carried by theFrequency Correction Channel (FCCH) of the Broadcast Control Channel (BCCH) of the GSMsignalling frame structure. The information travelling through the FCCH is transmitted at themaximum power since it has to be received by all terminals. This procedure takes place evenin absence of mobile terminals and this aspect is exploited in the installation, after a properelaboration, as a persistent basic element. This basilar aspect represents the starting point ofthe real performance.

Another interesting procedure is the reception of a call. This event is preceded by a connectionsequence that sends a signalling message on a common channel (paging channel), throughwhich the MT is warned about the incoming call. The MT recognizes its code on the pagingchannel and it makes a random access on the RACH (Random Access CHannel) using themaximum allowed power, since it does not know its distance from the serving BS. If thisprocedure is successful (i.e. there are not collisions with other transmitting MTs), the networktransmits through the AGCH (Access Grant CHannel) mapped on a beacon frequency. Theremaining procedure for the prearrangement of call reception is achieved through SDCCH(Stand alone Dedicated Control CHannel). Power control is another procedure that isactivated over the SDCCH in order to adapt the transmission power to the distance betweenthe MT and the BS. Other procedures are activated over the SDCCH and they are completedwhen a TCH (Traffic CHannel) is assigned for the effective phonic communication. Only atthis time the MT rings and this is an interesting aspect to be considered in the procedureof translation to audible frequencies. Indeed we have to adapt this fast mechanism to thepossibility of our auditory system that can be affected by temporal masking when the ear isstimulated by two successive sounds separated by less than 200 ms, (24), (25).

3.3 Radio frequencies to audible sounds translation procedure

In this subsection we intend to present the process of converting radio frequencies into audiblesounds.

First of all we have to keep in mind that the human auditory system is able to sense a rangeof frequencies between 20 Hz and 20 KHz, even if the upper limit tends to decrease with ageand thus most adults are unable to hear above 16 kHz. Moreover, the ear does not respond tofrequencies below 20 Hz but signals with lower frequencies can be perceived through body’ssense of touch, if they are characterized by a certain level of intensity.

If we just take into account GSM, it is already evident that the bandwidth offered by GSMcellular communication is much larger than the one defined by the human hearing range.Indeed GSM-900 offers a 25 MHz uplink and 25 MHz downlink, GSM-1800 offers a bandwidthof 75 MHz both in uplink and downlink, the theoretical bandwidth of the human ear isjust equal to 19980 Hz, that is 0.01998 MHz. If we also take into account that GSM-900and GSM-1800 provide respectively 124 and 374 channels, the total number of channelsoffered by the GSM standard is 498, each one of them corresponding to a carrier frequency.In the simplified hypothesis of just GSM-900 and GSM-1800 the best solution would be to


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f880 915925960 1710,2 1784,81805,2 1879,8

1900 1980 20102025

21702110

{ 85 MHz{ 750,2 MHz

GSM-900 UL

GSM-900 DL

GSM-1800 DL

GSM-1800 ULUMTS FDD-WCDMA

UMTS TDD-WCDMA

(MHz)

{ 10 MHz { 20,2 MHz { 30 MHz{ 20,4 MHz

Fig. 4. GSM and UMTS frequencies allocation.

f880 915925

9601710,2

1784,21805,2

1879,81900

19802010

2025

2170

2110GSM-900 UL

GSM-900 DL

GSM-1800 DL

GSM-1800 ULUMTS FDD-WCDMA

UMTS TDD-WCDMA

(MHz)

20000

f (Hz)

20

{Audible

Range

Fig. 5. Assumed relation between audible band and GSM and UMTS frequencies.

convert each carrier frequency into an audible frequency. The overall distribution of cellularfrequencies for both GSM and UMTS is shown in figure 4.

By observing this figure it is evident that there are large frequency gaps that imply importantgaps in an eventual linear conversion into the audible band. This can represent a problemsince the audible range is very small compared to RF range, and this type of conversion wouldcause a noticeable loss of useful Audio Frequencies (AFs).

For this reason, in order to not lose audio bandwidth, we assumed to not consider the gaps inthe RF range of interest while plotting the line corresponding to the relation between AFs andRFs, thus obtaining a conversion as roughly shown in figure 5.

As a consequence of our assumption we obtain 7 different linear relations between RFs andAFs. These relations has been computed as follows:

1. First of all we computed the equation of the line shown in figure 6 where the upper limitof the x-axis is now equal to the highest RF minus the total amount of frequency gap. In


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f880 2170-915,8 (MHz)

10000

f (Hz)

40

{Audible

Range

Fig. 6. Conversion procedure.

these procedure we were obliged to make our first aesthetic assumption concerning therange of AFs to be chosen. Indeed, even if the whole audible range was theoretically to beassumed for the conversion, we decided a reduction between 40 Hz and 10000 Hz, becauselower frequencies are hard to be reproduced with medium quality devices, while higherfrequencies than 10 KHz may result in unpleasant sensations for the human ear.

2. Once the first line equation has been found, we had to take into account that the highestAF computed for the highest RF of the first band (i.e. GSM-900 UL) is also the lowestAF corresponding to the lowest RF of the seconf RF band (i.e. GSM-900 DL). Indeedconsidering the first band we have:

ymax = 0.02661 · 10−3· 915 · 10−3

− 23.38 = 0.967 (1)

While taking into account the second band we had to force this relation:

ymax = 0.02661 · 10−3· 1710.2 · 10−3

+ b = 0.967 (2)

This way we found the new constant term value.

3. The same procedure described at point 2. was followed for the other bands.

The complete list of relations found following the previously described procedure is presentedbelow.

y = 0.02661 · 10−3x − 23.28 GSM-900 UL

y = 0.02661 · 10−3x − 23.67 GSM-900 DL

y = 0.02661 · 10−3x − 43.61 GSM-1800 UL

y = 0.02661 · 10−3x − 44.15 GSM-1800 DL

y = 0.02661 · 10−3x − 44.69 UMTS TDD and FDD WCDMA

y = 0.02661 · 10−3x − 45.48 UMTS TDD-WCDMA

y = 0.02661 · 10−3x − 47.75 UMTS FDD-WCDMA

For a first implementation of RF Sounding we used Agilent HP 8592B Spectrum Analyzershown in figure 7. The device can be connected to an elaboration unit through a IEEE488 interface commonly called GPIB (General Purpose Interface Bus) interface, (32). Free


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Fig. 7. Agilent HP 8592B Spectrum Analyzer.

Windows utilities that help making and recording research-quality measurements withGPIB-based electronic test equipment are available on the internet. A script written inC-language has been developed to ask the spectrum analyser to take and send its measuresonce every T seconds, where T can be chosen depending on the purpose of the installationplacement and eventually the electronic music composer needs.

4. Localization through a WSN

This section is intended to provide more insight motivations and functioning of WSNs forlocalization purposes.

WSNs are distributed networked embedded systems where each node combines sensing,computing, communication, and storage capabilities. The nodes constituting the network areinexpensive, consisting of low power processors, a modest amount of memory, and simplewireless transceivers. These properties allowed WSNs to become very popular in recent yearsfor applications such as monitoring, communication, and control. One of the key enabling andindispensable services in WSNs is localization (i.e., positioning), given that the availability ofnodes’ location may represent the fundamental support for various protocols (e.g., routing)and applications (e.g., habitat monitoring), (26).

The novelty we introduced with this project in the field of WSNs, is the application of one oftheir main functionalities such as localization, in the field of artistic installation.

In general there exists a variety of measurement techniques in WSN localization such asangle-of-arrival (AOA) measurements, distance related measurements and RSS profilingtechniques. Distance related measurements can be further classified into one-way propagationtime and round trip propagation time measurements,the lighthouse approach to distancemeasurements, received signal strength (RSS)-based distance measurements and timedifference-of-arrival (TDOA) measurements, (27).

For a first implementation of our specific application we used sensor nodes from Memsic(originally Crossbow) called Crickets, (28), (29), (30). Cricket nodes are small hardwareplatform consisting of a Radio Frequency (RF) transceiver, a microcontroller, and otherassociated hardware for generating and receiving ultrasonic signals and interfacing with ahost device, figure 8. Depending on their configuration, there are two types of cricket nodes:beacons and listeners. Cricket beacons act as fixed reference points of the location system andcan be attached to the ceiling or on a vertical wall depending on the application, (28), (29),while cricket listeners are attached to objects that need to obtain their location.


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Fig. 8. A Cricket hardware unit.

Java Applications

(clientlib)

Processor

(cricketdaemon)

Listener Interface

(cricketd)

TCP 5001

TCP 2947

Host Software

serial port

Fig. 9. Cricket software architecture.

Each beacon periodically transmits a radio frequency (RF) message containing beacon-specificinformation, such as beacon-ID, beacon coordinates, etc. At the beginning of the RF message, abeacon transmits a narrow ultrasonic (US) pulse that enables listeners to measure the distancesto the beacons using the time difference of arrival between RF and ultrasonic signals. It isworth noting that the ultrasonic pulse does not carry any data in order to reduce beaconpower consumption and ultrasonic hardware complexity.

Cricket listeners passively listen to beacon transmissions and compute distances to nearbybeacons. Each listener uses these distances and the information contained in the beacon RFmessages to compute their space position.

When beacons are deployed, they do not know their position. To compute beacon coordinates,it is possible to move around a cricket listener that collects distances from the beacons to itself.Using these distances, a host attached to the listener computes inter-beacon distances; thelistener has to collects enough distances such that the set of computed inter-beacon distancesuniquely define how the beacons are located with respect to each other.

The software for Cricket (embedded software as well as higher-layer software that runs onlaptops/handhelds) is under an open source license and can be used for education, research,and commercial purposes as long as the requirements in the copyright notice are followed.The cricket embedded software is written in TinyOS (31), an open source, BSD-licensedoperating system designed for low-power wireless devices. The software package includesa library to help developers create Cricket applications in Java. Cricket software architectureis shown in figure 9. At the lowest layer, cricketd allows a Cricket host device to accessthe Serial Port API to configure low-level Cricket parameters and obtain raw measurementsfrom the Cricket hardware device. CricketDaemon is a server application that connects


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Fig. 10. MicaZ mote.

to cricketd to filter and process raw Cricket measurements to infer the listener’s spatiallocation and compute its position coordinates. The algorithm lying behind this procedure isbased on the localization approach presented in (30). In a nutshell this algorithm combines thebenefits of a passive mobile architecture (e.g. scalability, no need of a network infrastructure)with advantages of an active mobile system. This procedure is based on 3 main algorithms:

• outlier rejection: it eliminates bad distance samples;

• extended Kalman filter (EKF): it maintains the current and predicted device states andcorrects the prediction each time a new distance sample is obtained;

• least-squares solver (LSQ): it minimizes the mean-squared error of a set of simultaneousnon-linear equations.

Java applications may access the processed location information via the Java Cricket clientlibrary (Clientlib), which interfaces between the application and the CricketDaemon.

For our specific application we provided a software with a minimum amount of localizationdata elaboration based on standard deviation. This was because data coming from theunderlying level appeared to be enough stable and rapid for a real time elaboration suchas the one required by RF Sounding.

We also used Memsic MicaZ motes to provide for a wireless connection between the listenerand the central elaboration unit. A MicaZ mote is shown in figure 10. Basically a MicaZ isconnected to a listener, while the other one is connected to the central elaboration unit, themotes provide a transparent connection between the listener and the central elaboration unit.This way the user bringing a listener is free to move inside the installation area.

5. Open sound control protocol

In this section we want to provide for a brief overview of methods used to transmitlocalization data and radio spectrum information to the central elaboration unit shownin figure 1. In particular we focus on the use of Open Sound Control Protocol anopen, transport-independent, message-based protocol developed for communication amongcomputers, sound synthesizers, and other multimedia devices, (33), (34). OSC was originallydeveloped, and continues to be a subject of ongoing research at UC Berkeley Center for NewMusic and Audio Technology (CNMAT).


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Spectrum Analyser

+

Elaboration Unit

WSN

+

Elaboration Unit

Central

Elaboration

Unit

OSC Client

OSC Client

OSC Server

OSC packets

via IP

Fig. 11. Communication configuration.

OSC provides some very useful and powerful features that were not previously availablein MIDI, including an intuitive addressing scheme, the ability to schedule future events,and variable data types, (35). Moreover the address space could be expanded through ahierarchical namespace similar to URL notation. Using this type of addressing allows differentprograms to create its own address hierarchy so that the same objects will not need the sameaddresses from program to program.

The main characteristic that was really appealing from our point of view is that OSC is atransport-independent protocol, meaning that it is a format for data that can be carried acrossa variety of networking technologies.

OSC data are basically organized into messages, which consists of the following:

• a symbolic address,

• a message name,

• the message payload.

With respect to the well known MIDI protocol, OSC is transmitted on systems witha bandwidth in the 10+ megabit/sec, that is almost 300 times faster than MIDI (31.25kilobit/sec). Moreover precision is improved and it is much easier to work with symbolicnames of objects rather then complicated mapping of channel numbers, program changenumbers and controller numbers as in MIDI. On the other hand it has to be noticed that OSCcan not replace MIDI, due to missing automatic connect-and play (or plug-and-play) concept,that is connected devices (via Ethernet, WLAN, Bluetooth etc) cannot scan each other andlearn about each others capabilities, moreover a file format such as standard MIDI file forexchange of data does not exist.

Any application that sends OSC Packets is an OSC Client; any application that receives OSCPackets is an OSC Server. An OSC server must have access to a representation of the correctcurrent absolute time. OSC does not provide any mechanism for clock synchronization butassumes that the two interacting systems will provide a mechanism for synchronisation. Timetags eliminate jitter introduced during transport by resynchronizing messages in a bundle andsetting values for when they should take place.

Given the main advantages coming from the use of the OSC protocol we decided to assumethe flexible configuration shown in figure 11.


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RF frequency

content

Magnitude

spectrum

Spectrum

analyzer

+

Elaboration

unit

Sound

elaboration

unit

Additive synthesis

of sinusoidal components

Fig. 12. Sound production for educational purposes.

The Central Elaboration Unit is equipped with Max 5, (36), a visual programming language formusic and multimedia that is used in our application in order to implement sound synthesisand elaboration as well as sound spatialization as a function of RFs translation and localizationdata. The basic language of Max is that of a data-flow system: Max programs (called patches)are made by arranging and connecting building-blocks of objects within a patcher, or visualcanvas. These objects act as self-contained programs (in reality, they are dynamically-linkedlibraries), each of which may receive input (through one or more visual "inlets"), generateoutput (through visual "outlets"), or both. Objects pass messages from their outlets to theinlets of connected objects.

For our purpose of communication through OSC we exploited the use of two main Maxobjects: udpsend and udpreceive that allow to realize the configuration shown in figure11.

6. Sound synthesis and real time processing

In this section we provide for an overview of the main algorithms and techniques used togenerate and to spread the sound all over the installation area.

A first distinction has to be done considering the possible applications of the project. Indeed itis clear that if the installation is used with educational purposes, than the sound to be spreadthrough loudspeakers has to represent RFs behaviour as close as possible. On the other handif the project is considered as an artistic installation rich in technological innovations, than thesound reproduced must be generated taking into account aesthetic considerations.

Let us consider the first applicative field. While using RF Sounding with educational purposeswe have to reproduce RFs behaviour such that their effects should be clearly understood bythe users. Having this in mind, we decided to assign each translated frequency to a sinewave, whose amplitude is thus defined by the magnitude corresponding to that frequency andcomputed by the spectrum analyser. Two schemes to better explain this process are presentedin figures 12 and 13. The latter is referred to a particular of the procedure of conversion inthe Max patch that has been developed. It has also to be noticed that the proportionalitybetween amplitude of the audible signal and emitted power is of fundamental importance tounderstand how operations on a cellular phone influence the electromagnetic pollution. Theeffect of this procedure can be easily imagined in the case of mobile switching on and callreception procedures described in section 3.

When the installation is used for artistic purposes it becomes an interesting opportunity formodern music composers to introduce a proper signal processing on revealed RF signals. Thisway the installation becomes a new instrument for which new music can be composed.


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OSC message

unpack

i-th

frequency

i-th

amplitude

X

i+1-th

frequency

i+1-th

amplitude

X

...... ......

+

s(t) Audible Signal

Fig. 13. Max like scheme in sound production for educational purposes.

Basing on our aesthetic point of view we decided to synthesize the sound through 3 maintechniques:

1. white noise filtering with resonant filters whose center frequency is defined by revealedRFs and whose Q-factor, (37) is a function of the measured amplitudes;

2. FM parallel modulations with one carrier and one modulating signals that are added toproduce the final result, (38);

3. Additive synthesis of sinusoidal components found as in the educational case plusgranular synthesis, (39) where envelope and silence interval of duration are defined a afunction of revealed frequencies.

It is worth noting that given a set of frequencies and values corresponding to amplitudes,these sets can be used for sound synthesis in an almost infinite number of ways includingAmplitude Modulation, Phase Modulation, filtering of complex signals and so on.

We decided to introduce a random variation between the 3 methods of synthesis previouslylisted, maintaining the randomicity between 3 and 5 minutes. It has to be noticed that thereproduced sound is pretty much variable because of different operations that are exploitedby the MT or the BTSs acting on the installation area.

We also exploited the localization data coming from the WSN to produce multichannelspatialiation of sound. While taking into account this procedure, many parameters can bevaried, (41), (42), (43):

• power of all the signals emitted in the environment,

• sound motion,

• number of loudspeakers involved in sound emission in a certain instant,

• crossfade envelope between two or more channels,

• residual power of loudspeakers not directly involved in main sound emission.


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For what concerns spatialization algorithms it has to be noticed that our installation allows acountless number of possibilities.

A first characterization has to be done as a function of the user’s motion inside the equippedarea while the installation is used for educational purposes. In this case we made an analysison the background RF Spectrum with respect to RFs produced by active operations of the userinside the area. Indeed when the spectrum is only defined by periodic downlink operations,the sound produced is not spatialized but instead it is uniformly diffused around the areawith a low intensity. On the other hand when user’s MT makes its own operation, the soundis spatialized such that to give the user’s the impression of being followed.

Obviously when the installation is used with artistic purposes the possibilities allowed bythe sound diffusion system can be exploited with a major freedom. In this case we fixed athreshold for the user’s speed. Below this threshold we established the sound diffusion systemto emit only a low circular spatialized sound. This is achieved by implementing the soundcrossfade only between adjacent loudspeaker. The envelope is characterized by sinusoidalpanning curves in order to avoid too rapid sound variations between channels. It has to benoticed that this choice requires the introduction of at least one element of randomicity onsound speed in order to avoid an unpleasant ”dance” effect on sound motion.

When the user is moving faster we assumed to spatialize the sound with the followingmethods:

• diagonal motion between single loudspeakers,

• motion between pairs of loudspeakers,

• slow motion between three loudspeakers with respect to a single loudspeaker or a pair ofloudspeakers such that to concentrate sound intensity in a certain point in the space,

• offeset variation between loudspeakers not directly involved in sound emission.

It is worth noting that all previously described mechanisms are automated as a functionof user position and motion, but also a random element is introduced in order to vary theperformance result.

We want also to underline that although the installation is flexible and can be realized bothindoor and outdoor, it requires the study of the impulse response of the environment andsound diffusion system characteristics.

7. Web interface

The project provides a Web interface in order to provide for a widespread diffusion of theinstallation’s acoustic results as well as to allow the users enjoying the equipped space torecord their performance and eventually use the result for instance as a ring tone. This ispossible by leaving the MT just below the antenna connected to the spectrum analyser fora few seconds. This way the installation produces a sort of audio signature that is quitespecific for each MT since both transmission power and RFs change as a function of the mobileoperator furnishing the service as well as the specific brand and model of the MT itself.


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This generated ring tone is associated to the user who can download it by logging in theinstallation website. This operation can be done in the installation area that is provided witha WiFi access.

8. Conclusions and future works

In this chapter an innovative project integrating technologies and experimental music hasbeen described. RF Sounding is based on the most recent technological innovations that areexploited in an unusual fashion and it focuses on the creation of an interactive installation witha double aim, to increase users’ awareness of the spectral occupancy in the cellular networksbands and to provide for a spectral phenomena aesthetic elaboration in order to produce asounding experience.

A lot of improvements can be achieved on this project. From the WSN point of viewit is important to develop a passive localization system through the exploitation of RSSIinformation as in multistatic RADAR, (44), (45), this way the user is relieved of bringing anexternal node inside the equipped area. Still concerning the technological aspect we wantto make reproducible also other communication standards such as Wifi, WiMax, Zigbee andBluetooth etc.

On the artistic point of view, we want to improve the installation’s adaptability and versatilityto different musical contexts, simplicity and rapidity in bringing changes in events, stabilityof the entire system and overall sound quality.

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Management of Technological Innovation in Developing andDeveloped CountriesEdited by Dr. HongYi Sun

ISBN 978-953-51-0365-3Hard cover, 312 pagesPublisher InTechPublished online 21, March, 2012Published in print edition March, 2012

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It is widely accepted that technology is one of the forces driving economic growth. Although more and morenew technologies have emerged, various evidence shows that their performances were not as high asexpected. In both academia and practice, there are still many questions about what technologies to adopt andhow to manage these technologies. The 15 articles in this book aim to look into these questions. There arequite many features in this book. Firstly, the articles are from both developed countries and developingcountries in Asia, Africa and South and Middle America. Secondly, the articles cover a wide range of industriesincluding telecommunication, sanitation, healthcare, entertainment, education, manufacturing, and financial.Thirdly, the analytical approaches are multi-disciplinary, ranging from mathematical, economic, analytical,empirical and strategic. Finally, the articles study both public and private organizations, including the serviceindustry, manufacturing industry, and governmental organizations. Given its wide coverage and multi-disciplines, the book may be useful for both academic research and practical management.

How to referenceIn order to correctly reference this scholarly work, feel free to copy and paste the following:

Claudia Rinaldi, Fabio Graziosi, Luigi Pomante and Francesco Tarquini (2012). RF Sounding: GeneratingSounds from Radio Frequencies, Management of Technological Innovation in Developing and DevelopedCountries, Dr. HongYi Sun (Ed.), ISBN: 978-953-51-0365-3, InTech, Available from:http://www.intechopen.com/books/management-of-technological-innovation-in-developing-and-developed-countries/rf-sounding-generating-sounds-from-radio-frequencies

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